Abstract: The cause of the extreme torrential rain event which occurred in Hebei Province during 3~5 August 1996 has been analysed using satellite and conventional data. The results show that this event appeared in favorable area nearby northwestern side of subtropical high under strong meridional circulation, and it was caused by two mesoscale convective cloud clusters directly. The interaction between the southern low level jet and weaker cold air of ground layer from northern North China led to initiation and development of the cloud clusters.